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Flux activity with SAC305

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jh0n!

#35757

Flux activity with SAC305 | 27 July, 2005

This may be completely normal, but I'm not used to seeing this with our old SnPb. I'm setting up reflow profiles for a SAC305 alloy, and it seems that on some of our larger pads, the flux seems to pool in the center. Is this perhaps a sign that I'm bringing the temperature up too high/low for too long or not long enough? I peak at 244, and hold above liquidus for about 45 seconds or so, which is in line with the manufacturer's spec.

Here's a few pictures to show what I'm talking about: http://tinypic.com/9i8v2x.jpg http://tinypic.com/9i8vb8.jpg http://tinypic.com/9i8voj.jpg

Thanks in advance for any help!

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Ken

#35773

Flux activity with SAC305 | 27 July, 2005

If no-clean...then this seems "relatively" normal. You could try and extend your peak and duration, however, manufacturers are adjusting their chemistry to survive these normal temperatures (up to 260C and 30 seconds within 5C of peak). You will have less "burn-off" at elevated temps. I don't see any issue. If solder quality is there then this is purely cosmetics.

But holy crap! Can you get those rows of resistors any closer together?

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jh0n!

#35782

Flux activity with SAC305 | 28 July, 2005

That's pretty much what I figured - just wanted some external verification if possible.

And don't so much as BREATHE that around here. I'm just waiting for engineering's *next* bright idea. ;)

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Cmiller

#35785

Flux activity with SAC305 | 28 July, 2005

What stencil reduction are you using so the resistors dont bridge??

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jh0n!

#35789

Flux activity with SAC305 | 28 July, 2005

On chips, none - 1:1. Those are 1206 chips, either .010 or .015" between them. I've never seen one bridge. Some *rare* billboarding. That's it.

*shrug*

These QFNs, tho....

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